1. Field of the Invention
This invention relates to methods for generating x-rays by using laser driven sources for high-energy radiography.
2. Description of the Related Art
Referring to FIG. 1, a conventional x-ray machine 10 is shown. The electron accelerator bremsstrahlung source 12, for example, a flash x-ray (FXR) source, creates high velocity electrons 8 directed toward a target 14. These electrons have an energy level of 15 MeV. The typical target 14 consists of several layers of materials sandwiched together with a thick radiator layer of, for example, tantalum 22 (1 mm thick). As the high velocity electrons pass through the target 14, bremsstrahlung x-rays 16 are formed and pass through the object 18 to form an image on detection plate 20. One disadvantage of the FXR source is that the source needs to be close to the target when generating the high-energy electrons, because these electrons quickly dissipate over short distances. Since these electron accelerator sources are extremely large, there is a limit to the number of multiple axis views that can be performed on an object 18 at one time. If the tests performed on the object are destructive, for example, an impact or explosive experiment, then exposure to only one or two detection plates 20 is possible.
In addition, the xe2x80x9cburstxe2x80x9d of high-energy electrons usually lasts a long period of time, such as tens of nanoseconds, causing a substantial amount of scattered x-rays that will affect the exposure of the detection plates. Also, it may take a long time for the energy fields created by the electron accelerator source to dissipate before another procedure can be performed. Therefore, there is usually inferior spatial and temporal resolution of the imaged object by using conventional electron accelerators.
The present invention discloses a method and apparatus for imaging an object by generating laser pulses with a short-pulse, high-power laser. When the laser pulse strike a conductive target, Bremsstrahlung radiation is generated such that hard ballistic high-energy electrons are formed to penetrate an object. A detector located on the opposite side of the object detects these electrons. The detector could be time gated in order to detect specific ballistic high-energy electrons.
An object of the invention is to form hard x-rays from the bremsstrahlung radiation to image objects.
Another object of -the invention is use multiple laser pulses to image an object in motion, for example, an exploding or imploding object.
Another object of the invention is to generate multiple laser pulses that can be directed down different tubes using mirrors and beam splitters so that each laser pulse will image a different portion of the object.